The present invention relates to a brake system for automotive vehicles with electric drive. In particular, the present invention relates to a brake system which is operable by an actuating pedal and includes at least one electric drive motor as well as hydraulic friction brakes which are connected to a master brake cylinder. Such brake systems also include a device for determining the pressure prevailing in the master brake cylinder, an electronic controller to which the output signal of a sensor determining the actuating condition of the actuating pedal is fed, and a control device controlling the electric drive motor(s).
A brake system of this kind is described in the article "Design of a Lightweight Braking System for Electric Cars" (SAE-paper 920649 of January 1992). In this system, the hydraulic friction brakes are connected to the corresponding pressure chambers of the master brake cylinder via the intermediary of valve assemblies which are each formed by an electromagnetically operable bypass valve as well as by a differential-pressure control valve which is operable by the pressure prevailing in the hydraulic pressure chamber of the master cylinder. The two valves, preferably, are connected in parallel. Electromagnets, which actuate the bypass valves, are driven by the control devices which control the electric drive motors.
The pedal characteristics of this known system are considered disadvantageous. These pedal characteristics conform only very imperfectly to the pedal characteristics of a standard passenger car and exhibit a broad hysteresis and two portions of different gradients resulting in a discontinuous pedal feeling. Further, the known brake system cannot take into account the varying retarding power of the electric drive motors. Also, the separate mounting of the master brake cylinder and the valve assemblies requires considerable space.